TypeScript

References

• Learn TypeScript in Y Minutes

• TypeScript Deep Dive

Tools

• A minimal Yeoman Generator for creating NodeJS modules using TypeScript

TypeScript Notes/Tips/Patterns

• Scope: by default members in a class are public

• Enum: an enum is a way of giving more friendly names to sets of numeric values

  • String enum: use custom Type. See more here.

• Do we put return type when defining function? Yes. getSum(a: number, b: number): number {}

• Type assertion: (<string>someValue).length;

• We have static, readonly

  • const is for variable. No one can modify it after assigned.

  • readonly is for property (class property to property in interface). Properties must be initialized at their declaration or in the constructorSee here

  • static must be class member.

• Function overload, this is possible in TypeScript but it's not supported by JavaScript.

• Default parameter: getSum(data: number[], skipNegative: boolean = false)

Favor getter over method in TS

Type: How to declare type to object property and key?

var stuff: { [key: string]: string; } = {};
stuff['a'] = ''; // ok
stuff['a'] = 4;  // error

Type: type of array item based on index

• public label(row: {0: string, 1: number}): string {

• var t:[number, string] = [1, "message"]

Use Destructuring (FP concept)

// pick only the data we need using destructing
// Function signature: getAccountInfo(): {balance: number; cardStatus: string; cardNumber: string; cardHolder: string}

// before:
.then((response:any) => {
        const data = this.getAccountInfo()
        return {
          balance: data.balance,
          cardStatus: data.cardStatus
        };

// after
.then((response:any) => {
        const {balance, cardStatus} = this.getAccountInfo()
        return {
          balance,
          cardStatus
        };

Be careful: it's too easy to create private member

If the data is NOT used anywhere, don't put private.

constructor(private data?: any) {
      this.model = this.extract(data);
    }